She was actually a vegetarian for a while. She moved back to NC a couple years ago, and was finally able to have NC pulled pork barbecue again... only to discover soon after that she was now allergic to it.

But I guess she still eats chicken, so she's not forced to be completely vegetarian.

I actually don't like the rubber sheet analogy; it makes people have these ideas about spacetime being athing that gets deformed. Which it could be, but there's zero reason to think so.

__________________The miracle of the appropriateness of the language of mathematics for the formulation of the laws of physics is a wonderful gift which we neither understand nor deserve. -Eugene Wigner

I actually don't like the rubber sheet analogy; it makes people have these ideas about spacetime being athing that gets deformed. Which it could be, but there's zero reason to think so.

We need a better analogy.

Possibly one that doesn't start with something being somewhere in something else. It seems easy enough to make analogies for time that don't assume time, just by thinking of it as a space dimension. But what kind of analogy could you create for space that doesn't involve ... space?

I like to think of it like kind of adjustments you have to make for navigation even here on Earth - paths that seems straight are actually curved over long distances. Likewise, gravity 'bends' locally straight paths, so for example the Moon isn't held near the Earth by some force or tether, it's following the path it would normally follow given its velocity, etc. It's the path that's bent.

I conceive of it as much like a magnetic field, except it isn't polar and doesn't attract on ferrous materials or other magnetic fields, but rather mass. Otherwise, the fields would seem very similar to me. It's easier for me to imagine it as a volume with puckers and "arms" than as a deformed plane. I just imagine bi-directional field lines in holographic presentation.

__________________Chained out, like a sitting duck just waiting for the fall _Cage the Elephant

It's not all that good an analogy, but it's slightly helpful to consider how a two dimensional surface which we regard as flat (or at least 'almost flat') displays strange 'non-flat' properties.

Imagine the Earth without any mountains or oceans so that the surface is as flat as possible. Now any two straight lines you draw on the surface - even ones which you try to draw parallel to each other - will cross at two places. Think of lines of longitude on the surface of the Earth which all meet at the poles. Some people, when you tell them this, point out that lines of latitude do not cross - but that is because all of them, except the equator, are not straight lines - they are curves.

ETA: or what Kael said, except I waffled more.

Because we are unable to imagine in four dimensions (and we're not even that good at imagining in three dimensions) it's pretty near impossible, as far as I know, to get an intuitive grasp of how space time is distorted by mass.

I think the best we can do is say that with masses up to that of a typical star, and velocities that are typical for stars and planets, then the curvature of space time is just enough to make things move along the same paths they would using Newton's concepts of gravitational force - and remember that with much larger masses or much higher speeds then things become weirder and we need more complex mathematics to model the weirdness.

I actually don't like the rubber sheet analogy; it makes people have these ideas about spacetime being athing that gets deformed. Which it could be, but there's zero reason to think so.

So when people talk about the squashing and stretching of spacetime, what's the other option besides distorting spacetime?
Along the lines of that, when spacetime expands causing light to 'cool' down as seen in the CMB, where does the energy from that light go? (or is this one of those weird reference frame things).

I actually don't like the rubber sheet analogy; it makes people have these ideas about spacetime being athing that gets deformed. Which it could be, but there's zero reason to think so.

So when people talk about the squashing and stretching of spacetime, what's the other option besides distorting spacetime?

Distances between objects get longer or shorter.

Quote:

Along the lines of that, when spacetime expands causing light to 'cool' down as seen in the CMB, where does the energy from that light go? (or is this one of those weird reference frame things).

Energy is not conserved in general relativity.

Remember: energy is the quantity conserved because the laws of physics do not change with time. But time in general relativity is just a coordinate - it has no real meaning. So what happens to the conservation laws...?

__________________The miracle of the appropriateness of the language of mathematics for the formulation of the laws of physics is a wonderful gift which we neither understand nor deserve. -Eugene Wigner

The experiments are really hard, and full of noise and unknown parameters.

__________________The miracle of the appropriateness of the language of mathematics for the formulation of the laws of physics is a wonderful gift which we neither understand nor deserve. -Eugene Wigner

(Sean Carroll is a pretty big name in cosmology, and right now works at Caltech. He has plenty of other opinions that are less backed by his qualifications, but are usually pretty rational. His posts also contain a lot of links to papers or blogs of other scientists in the field - well worth following up. )

__________________The miracle of the appropriateness of the language of mathematics for the formulation of the laws of physics is a wonderful gift which we neither understand nor deserve. -Eugene Wigner